If I'm not restricted to an regex:

my $ans = 1;
my $cnt = 0;
for (map {$cnt++ < 4 and
        $_=~/[0-9]+/ and $_ >= 0 and $_ <= 255 ? 1 : 0}
        split /\./, $ip)
{$ans &= $_};
[download]

Not super pretty, nor fast. But TIMTOWDI, as they say.

-Gryn